1. Field of the Invention
This invention relates to the preparation of novel geminal hydroxymethyl compounds from 9(10)-formylstearic acid and also the acyloxy derivatives of such compounds useful as primary plasticizers for polyvinylchloride (PVC).
2. Description of the Prior Art
A plasticizer is a material which is incorporated in a plastic and which functions to increase its workability and flexibility. The search for acceptable plasticizers has been a very active one. In 1934 about 56 plasticizers were being produced and from that time until about 1943, over 20,000 plasticizer compositions had been disclosed in the literature, 60 of which are among the 500 presently available (cf. Encyclopedia of Polymer Science and Technology, Vol. 10, John Wiley and Sons, Inc., 1969, p. 230).
Primary plasticizers are plasticizers which are miscible with the polymer in amounts sufficient to impart the desired characteristics to the final product without exuding. Secondary plasticizers are those which are not soluble in the polymer in the desired amounts and, therefore, must be used in smaller amounts in combination with another more compatible plasticizer. "Compatibility" is the term used to describe the ability of two or more substances to mix with each other to form a homogenous mixture. The desired plastic product is formed by vigorously mixing polymer and plasticizer at elevated temperature (about 160.degree. C. for polyvinylchloride) until "fusion" takes place. Fusion is the mechanism by which plasticizer and polymer become a homogenous mixture and, therefore, the ease of fusion is directly related to compatibility.
It is generally believed that in PVC, ease of fusion tends to decrease with increasing molecular size and decreasing polarity, and that addition of a carbon atom linkage to the plasticizer molecule causes a reduction in its compatibility for PVC (Encyclopedia of Polymer Science and Technology, supra, p. 250). Moreover, it would be expected that the addition of several carbon atoms would reduce compatibility even further.
The types of organic plasticizers in general use are liquids having moderately high molecular weights and include esters of carboxylic acids, esters of phosphoric acids, hydrocarbons, halogenated hydrocarbons, ethers, polyglycols, and sulfonamides. For reasons of compatibility, costs, process behavior, and performance, primary PVC plasticizers are generally limited to various dibasic acid and phosphate esters, epoxidized oils and resins, glycolates, mellitates, and polyesters of various dibasic acids with glycols, pentaerythritol derivatives, and sulfonates. Secondary PVC plasticizers are generally limited to various aromatic and mixed aromatic aliphatic oils, chlorinated paraffins, polyalpha-methyl styrene derivatives and esters of high molecular weight alcohols and organic acids (cf. Modern Plastics Encyclopedia, Vol. 50, No. 1A, 1973-74, pp. 254-266).
Dioctyl phthalate (DOP) is the most widely used primary plasticizer for polyvinylchloride and accounts for about 25% of the total market (Encyclopedia of Polymer Science and Technology, supra, p. 231). However, because of its volatility, migration, and incomplete biodegradability, DOP is suspect as a ubiquitous environmental contaminant. Other commercial plasticizers such as dioctyl sebacate (DOS) and dioctyl azelate (DOZ) suffer from high percent migration loss and poor compatibility with PVC. Any new plasticizer to be superior to DOP would have to show lower volatility, migration, and solvent extractability, as well as better biodegradability.
Efforts to find a substitute for DOP as a primary plasticizer have led to the investigation of derivatives of C.sub.18 unsaturated fatty acids.
Gruber et al., U.S. Pat. No. 2,332,849, teaches oxidizing and esterifying oleic acid to trans-9,10-dihydroxystearic acid methyl ester, which is then reacted with acetic anhydride to yield trans-9,10-diacetoxy stearic acid methyl ester.
Knight et al., J. Amer. Oil Chem. Soc. 36: 382- 388 (Sept. 1959), reports on a number of acyloxy and aryloxy compounds prepared from hydroxystearic acids.
Birum et al., U.S. Pat. No. 2,965,598, oxidizes the oxonation products of oleic acid and oleic acid esters and subsequently esterifies the resultant acids with a series of alcohols. The resultant esters have some utility as plasticizers.
Wheeler et al., U.S. Pat. No. 3,016,359, prepares plasticizers by an oxonation reaction similar to that of Birum et al., supra, and further teaches other C.sub.18 unsaturated acids as the starting material. Specifically taught are linoleic, linolenic, ricinoleic, and elaidic acids.
Bhatnagar et al., Ind. Chem. J., Ann., pp. 136-137 (1972), produces primary plasticizers by epoxidization of acetylated castor oil and by the acetylation of ricinoleates of glycerol.
Awl et al. [U.S. Pat. No. 3,983,067; J. Amer. Oil Chem. Soc. 49(4): 222-228 (1972); and J. Amer. Oil Chem. Soc. 51(5): 224-228 (1974)] reports on the plasticizing properties of ethylene acetals and dimethyl acetals from hydroformylated polyunsaturated vegetable oils and esters.
Frankel et al., J. Amer. Oil Chem. Soc. 52(12): 498-504 (1975), reports on a number of acyl esters from oxo-derived hydroxymethylstearates and compares them to various commercial plasticizers.
All of the prior art compounds discussed above exhibited some plasticizing properties. However, it has generally been observed that none of the heretofore known unsaturated fatty compound oxo-derivatives are significantly superior to DOP to successfully replace it as the leading plasticizer for PVC where improved permanence is desired. The primary problem in the art exists in combining good thermal stability and low migration and volatility with satisfactory compatibility.